INCORPORATION OF HISTORICAL AERIAL PHOTOGRAPHS AND LAND-USE INFORMATION INTO ENVIRONMENTAL SITE ASSESSMENTS

Historical aerial photographs and historical land-use documents coveri ng a period of 51 years were evaluated during the environmental site-a ssessment of Marine Corps Air Station (MCAS) El Toro, a military insta llation slated for closure and conversion to civilian usage. Although the photographs and documents could not, by themselves, prove the exis tence of contamination, information interpreted from them helped ident ify features and areas commonly associated with environmental contamin ation, such as abandoned landfills, drum-storage areas, trenches possi bly used for waste disposal, discolored soil, and surface-water discha rge from maintenance facilities. These features served as focal points for follow-on investigations. The investigation identified about 600 new sites of ''possible environmental concern,'' as defined by the cri teria specified for the project by the sponsor, and verified approxima tely 600 previously identified features. The project team interpreted 106 aerial photographs during the investigation. We also evaluated num erous land-use and planning documents. The final report of the investi gation includes annotated photographs depicting sites and areas of con cern for each of the 21 years of photographic coverage that were consi dered, land-use maps for five time periods, and surface-drainage maps for nine years. The investigation resulted in about 60 of the newly-id entified sites being scheduled for additional investigation.